Portabella mushroom tarte tatin

Bring a kettle to the boil. Put the dried wild mushrooms in a mug and cover with 150ml just-boiled water. Leave to steep for 10-15 minutes. Set a sieve over a bowl, then drain the mushrooms, reserving the mushroom stock.

Meanwhile, set an ovenproof frying pan (about 26cm base diameter) over a high heat. Add 30g butter, then 1⁄2 of the fresh mushrooms, flat-side down. Fry for 2 minutes, then flip each mushroom onto its open side. Add 3 tbsp water to the hot pan, then steam and soak the mushrooms for 2-3 minutes more. Transfer the mushrooms to a plate and repeat with 30g more butter, 3 tbsp water and the remaining fresh mushrooms. Preheat the oven to 220°C, gas mark 7.

Remove the pan from the heat. While still hot, add the remaining 20g butter, the sugar and 1⁄2 of the thyme leaves; stir to combine. Pour in any mushroom resting juices, then return the cooked fresh mushrooms to the pan, arranging some flat-side down and others flat-side up, in 1 snug layer. Push the drained wild mushrooms into the gaps. Season and scatter over most of the garlic.

Weigh 400g puff pastry (wrap and freeze the remainder for another occasion). On a lightly floured surface, roll out the pastry and cut into a circle slightly bigger than the pan. Lay the pastry over the mushrooms, tucking it in at the edges. Bake for 25-30 minutes until the pastry is puffed and golden.

About 10 minutes before the tart is ready, pour the reserved mushroom stock into a small saucepan. Add the remaining garlic and the thyme sprigs, then bring to the boil. Stir in the sherry, mustard and crème fraîche; season and simmer for 7-8 minutes. Once the tart is cooked, carefully pour any liquid from the base of the pan into the saucepan, then strain the liquid into a gravy jug.

Put a wide plate with a lip over the tart dish, then carefully invert the tart onto it and scatter over the remaining thyme leaves. Carve into quarters and pour over the sauce.